Neural progenitors and stem cells hold a great deal of promise as therapeutic tools in the treatment of neurologic and psychiatric disease. However, a great deal of knowledge regarding neural progenitor/stem cell biology needs to be obtained prior to their effective therapeutic utilization. For example, there are no reliable extracellular markers for neural stem cells to distinguish them from other cells in the mammalian brain. Previous studies have identified sets of genes that are uniquely expressed in neural progenitors and not more differentiated cells. However, the identification of mRNAs or mRNA fragments does not necessarily identify the sets of proteins that are actually expressed. Furthermore, very few of already identified genes predict proteins that are expressed at the cell surface, the most useful localization to serve as a cell-specific marker. The identification of cell surface proteins would not only facilitate the understanding of the biology of neural progenitors, but would also aid in the prospective identification of neural progenitors for studies of basic biology as well as therapeutic strategies. Modern proteomic approaches allow for the rapid identification of proteins differentially expressed in two populations of cells. It is the goal of this pilot study to determine whether a proteomic approach can be successfully applied to the study of neural progenitor cells. In the first set of experiments we will test the hypothesis that neural progenitors express specific sets of cell surface proteins. To achieve this, we will first determine whether neural progenitors express membrane proteins that are different from those expressed in more differentiated cells. Membrane proteins from neurosphere cultures derived from embryonic or postnatal mice containing stem and progenitor cells will be compared to proteins from more differentiated sister cultures. We will then compare results obtained with our previous results obtained using genomic methods. We will also determine whether neural progenitors derived from mice at different ages express different membrane proteins, as in vitro studies demonstrate they have different differentiation potentials. This study will aid in determining whether the stem/progenitor cells isolated at these different ages are different "kinds" of cells. After we identify candidate proteins, downstream studies will determine whether these molecules are potential cell surface markers for subsets of neural progenitors and whether they have important roles in neural progenitor biology using a combination of methods. It is anticipated that these pilot studies will pave the way for new avenues in the study of neural progenitor cell biology.